Situation: Clip One Above Center Too Lean - Center Is Too Rich. What Do I Do?

yuckfoo

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72 jet. I had the clip one above center and was getting high revs when I pulled the clutch in. Nothing super high just that the engine speed wouldn't come down with the clutch in sometimes. I checked for leaks, there are no leaks. I looked at the plug and it was what I would call "white" ... a very light gray. I put the clip in the middle and the plug turned very black, sooty and a bit wet on the ring in one place. I've not seen this sort of thing so far. There appears to be no middle ground here. One is too lean, the next is too rich. The only thing that has changed is I replaced both of my clutch gears.

The plug was showing white after an 8 mile ride, that's when I changed the clip to the middle. After about 24 more miles the plug is black.

How do I tune with these conditions?
 

Cannonball3

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I punch shims from drink cans using a center punch set. Punch the small(needle) hole first followed by the larger punch. They average .007” thick they work nicely to tune between needle slots. Just add them under the needle as needed to tune.
 

DieselTech

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That's a great tuning hack there! I never thought of that. I know you can buy different needle jet sizes & tip shape, but I'm unsure if there of a universal type or not.
 

yuckfoo

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I punch shims from drink cans using a center punch set. Punch the small(needle) hole first followed by the larger punch. They average .007” thick they work nicely to tune between needle slots. Just add them under the needle as needed to tune.
Makes sense. Thanks. What do you think about going back down to the 70 jet? (Currently at 72) It's hard to remember (it was a few weeks ago) but I think the 70 jet worked well, but the 72 seemed to work better, or, maybe I was following the advice of using the next higher jet after the jet that gives you your highest speed. But I've also been (accidentally) using two different spark plugs.

Today's ride after changing the clip was very lurchy. It ran better at WOT but even then I'd get a lurch or two.
 

yuckfoo

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That's a great tuning hack there! I never thought of that. I know you can buy different needle jet sizes & tip shape, but I'm unsure if there of a universal type or not.
yeah, I've been wondering if I'd benefit from a two stage needle.
 

Cannonball3

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Dont know what carb you are using but if its an NT, get a Bofeng. The needle is well profiled. They have run well
on all my engines with minimal fuss. Respond well to shimming and no four stroking. Generally run on the center
of 5 slots. A couple of shims fine tunes it. They are $9.99 on ebay.
 

yuckfoo

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That's a great tuning hack there! I never thought of that. I know you can buy different needle jet sizes & tip shape, but I'm unsure if there of a universal type or not.
I've seen a video that shows two types. One has two different tapers and the other had 3 or more... maybe five. My memory is ... um, what's that thing, ... oh yeah! Crap! 😝
 

DieselTech

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Yeah that bofeng carb that cannonball3 recommended, I've heard nothing but good things about them. There cheap & seem to perform better & easier to tune. I've heard at times there hard to find that carb.
 
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